EARTHQUAKES AND SEAQUAKES 



77 



fault which appeared at the time of the Assam earthquake of 

 1897 (Fig. 67). From this map it will be noticed that the upward 

 or downward displacement upon the perpendicular plane of the 

 fault is not uniform, but is subject to large and sudden changes. 

 Thus in order the measurements in feet 

 are 32, 0, 18, 35, 0, 8, 25, 12, 8, 2, 0. 

 The fault formed in 1899 upon the 

 shores of Russell Fjord in Alaska (Fig. 

 68) reveals similar sudden changes of 

 throw, only that here the direction of 

 the movement is often reversed; or, 

 otherwise expressed, the upthrow is 

 suddenly transferred from one side of 

 the fault to the other. Such abrupt 

 changes in the direction of the dis- 

 placement have been observed upon 



FIG, 69. Abrupt change in the direction 

 of throw upon an earthquake fault which 

 was formed in the Owens valley, Califor- 

 nia, in 1872. The observer looks directly 

 along the course of the fault from the left 

 foreground to the cliff beyond and to the 

 left of the impounded water (after a 

 photograph by W. D. Johnson). 



FIG. 68. Map giving the 

 displacements in feet 

 measured along an earth- 

 quake fault formed in 

 Alaska in 1899 (after Tarr 

 and Martin). 



many earthquake faults, and a particularly striking one is repre- 

 sented in Fig. 69. 



The block movements of the disturbed district. The displace- 

 ments upon earthquake faults are thus seen to be subdivided into 

 sections, each of which differs from its neighbors upon either side 

 and is sharply separated from them, at least in many instances. 

 These points of abrupt change of displacement are, in many cases 

 at least, the intersection points with transverse faults (Fig. 69). 



